1. Field of the Invention
The present invention relates to a thermosensitive recording material and a thermosensitive recording method. More specifically, the present invention relates to a thermosensitive recording material and a thermosensitive recording method, characterized in that thermosensitive recording can be done at a higher sharpness by means of a relatively simple process. The thermosensitive recording material in accordance with the present invention can be applied extensively as original plates for lithographic printing, OHP recording plates, original plates for electrostatic recording, original plates for magnetic recording, original plates for colored image recording and the like. In the present Specification, explanation will follow principally on the application thereof as an original plate for lithography printing.
2. Description of the Prior Art
As thermosensitive recording materials to be used in original plates for lithographic printing, for example, the following types have been known;
1. Presensitized (PS) Plate having a constitution wherein the surface of an aluminium plate is processed with graining and a thermosensitive layer is arranged thereon;
2. an original plate having a constitution wherein a photoconductive layer comprising zinc oxide and the like is arranged on a support such as paper; and
3. a directly imaging master having a constitution wherein the surface of a support is processed with a hydrophilic process.
Any of these original plates has the surface processed with a hydrophilic process, and can be engraved by depositing an ink-philic substance on the part corresponding to an image. At printing, a hydrophilic non-image part repels oily ink via dampening water, while an ink-philic image part receives oily ink because dampening water is not deposited on that part, whereby the image part and the non-image part are separately obtained thereby achieving lithographic imaging.
However, the discrepancy between so-called ink-philic and hydrophilic properties at the image part and non-image part is slight, so the volume of dampening water has great influence such that when there is a small excess of dampening water, the dampening water remains at the ink-philic image part which may therefore eventually repel oily ink. On the contrary, if there is a small deficiency of dampening water, the repulsion of oily ink from the non-image part is reduced thereby inducing problems such as the occurrence of greasing.
To overcome these problems, proposition has been made of water-less lithographic printing with no use of water (see, for example, Japanese Patent Laid-open Nos. 59-194895, 53-59508, 5369704 and 59-211051). For these original plates for lithographic printing processing machines exclusively for such original plates are required, a special developing process is required, and printing sharpness is poor.
The so-called direct processing technique has been known which can finish direct printing plates based on the information of computer imaging. The direct-processing technique is illustrated by those types using electrophotography for transcription, an etching type, a type employing a photosensitive mechanism via silver salts, and a type using photopolymers or the like. However, these methods comprise forming an image via light, and generating a printing plate through a wet process such as development, fixing, solubilization, hydrophilic process and the like. Thus, problems for these types are as follows;
1. a printing machine of itself should be of a larger type;
2. hands may be contaminated during the handling of chemical reagents such as developing solution, solubilizing solution, etching solution and the like; and
3. liquid waste is generated.
Thus, these methods are not suitable for use in offices.
Furthermore, it cannot be said that the printing plates prepared by these methods are suitable for printing without dampening water, although the plates may be suitable for general printing using dampening water.